This invention relates to fuel supply control systems suitable for use with combustors of water heaters, etc., and more particularly it is concerned with a fuel supply control system for effecting proportional combustion.
To enable combustion to take place in good condition, it is necessary to keep constant the fuel-air ratio of fuel-air mixtures. Particularly in combustors for effecting proportional combustion, it is essential that the fuel-air ratio be kept constant through the entire range of changes in the amount of heat of combustion which show variations in a wide range.
This type of combustion apparatus is shown, for example, in Japanese Laid-Open Utility Model Publication No. 89537/1979. The fuel supply control system disclosed in this Publication comprises a diaphragm of a minor area and a diaphragm of a major area, three chambers separated from one another by the two diaphragms, and a valve connected to the two diaphragms for controlling the opening of a fuel passage, the chamber adjacent the diaphragm of the minor area serving as a chamber of the fuel passage upstream of the valve, the chamber between the two diaphragms opening in a chamber downstream of the valve and the chamber adjacent the diaphragm of the major diameter being connected to a combustion air supply passage system.
The control system of the aforesaid construction has the disadvantage that the fuel-air ratio of the mixtures is easily influenced by errors in fabrication and assembly of the system and the parts located in its vicinity.